1. Exit Choose to view chapter section with a click on the section heading. ►The Study of SedimentsThe Study of Sediments ►Types of SedimentTypes of Sediment ►Continental Shelf SedimentsContinental Shelf Sediments ►Deep Ocean SedimentsDeep Ocean Sediments ►Sediments as Economic ResourcesSediments as Economic Resources Chapter Topic Menu

2. MenuPreviousNext 14 - 2 The Study of Sediments Chapter 14 Pages 14-3 to 14-8

3. MenuPreviousNext 14 - 3 Sediment Study Tools and Techniques nAs you would expect, modern oceanographers use tools far more sophisticated than those used a hundred years ago to study the ocean bottom. nHowever, some study methods have not changed much in decades because they’re simple and effective. The Study of Sediments Chapter 14 Pages 14-3 to 14-5

4. MenuPreviousNext 14 - 4 Sediment Study Tools and Techniques nWhen a scientist needs a large sample of the top sediment, the instrument of choice is the clamshell sampler (also known as a grab sampler).  The clamshell sampler has a set of jaws much like those you may have seen on earth-moving cranes.  The sampler descends to the bottom with the jaws locked open.  When it hits the sediment, the jaws unlock automatically or via a trip line. This allows them to close, scooping up a sample when the researcher hauls the sampler back up. The Study of Sediments Chapter 14 Pages 14-3 to 14-5

5. MenuPreviousNext 14 - 5 Sediment Study Tools and Techniques Clamshell Samplers and Operation The Study of Sediments Chapter 14 Pages 14-3 to 14-5

6. MenuPreviousNext 14 - 6 Sediment Study Tools and Techniques nThe clamshell sampler brings up a lot of material, but it does not reveal much about the different sediment layers. nA piston corer is an open tube on a cable that is dropped from a ship. nTo sample even deeper, scientists use drilling equipment on specialized research vessels. The Study of Sediments Chapter 14 Pages 14-3 to 14-5

7. MenuPreviousNext 14 - 7 Sediment Study Tools and Techniques Piston Corers and Operation The Study of Sediments Chapter 14 Pages 14-3 to 14-5

8. MenuPreviousNext 14 - 8 Sediment Study Tools and Techniques nScientists also study sediments using seismic reflection.  An air gun transmits sound waves into the water, which penetrate into the seafloor.  Some reflect back to the ship off the transition between different rock or sediment layers.  The waves’ return speed depends on the density of the material they travel through.  Therefore, the signal can yield detailed information about the geologic structure and composition of the ocean floor sediments and underlying rocks.  Marine geologists commonly use this method when looking for oil and gas. The Study of Sediments Chapter 14 Pages 14-3 to 14-5

9. MenuPreviousNext 14 - 9 Sediment Study Tools and Techniques Air gun Bottom profiling using seismic refraction. The Study of Sediments Chapter 14 Pages 14-3 to 14-5

10. MenuPreviousNext 14 - 10 Stratigraphy and Paleoceanography nSedimentation is an ongoing process. Sediments from different sources constantly enter the ocean and settle to the bottom.  Because of this, at one time scientists expected that the sea bottom would tell them about the earliest days of the Earth.  In the 19th century, most scientists thought that ocean sediments would be very thick throughout the ocean basins.  Some hypothesized that perhaps a billion years lay buried in the sediments. The Study of Sediments Chapter 14 Pages 14-6 to 14-8

11. MenuPreviousNext 14 - 11 Stratigraphy and Paleoceanography nIn reality there is little or no sediment on the mid-Atlantic ridge, or any other seafloor spreading ridge.  The plate tectonics theory explains this.  The crust is new, little sediment has had a chance to fall onto it.  As new ocean floor moves away from the ridge, it ages and accumulates sediment.  Sediment thickness increases with distance from the ridge.  When it finally reaches a trench, the seafloor subducts. Subduction destroys old ocean crust, so there are no sediments on the ocean crust that are dated older than 200 million years. The Study of Sediments Chapter 14 Pages 14-6 to 14-8

12. MenuPreviousNext 14 - 12 Stratigraphy and Paleoceanography Plate motion at a mid-ocean ridge. The Study of Sediments Chapter 14 Pages 14-6 to 14-8

13. MenuPreviousNext 14 - 13 Stratigraphy and Paleoceanography nThe study of sediment layers is called stratigraphy.  Scientists use deep-sea stratigraphy to look for clues, such as rock composition, microfossils, deposition patterns, and other physical properties.  Based on these clues, scientists estimate the age of the sediment layers and draw conclusions about the past. The Study of Sediments Chapter 14 Pages 14-6 to 14-8

14. MenuPreviousNext 14 - 14 Stratigraphy and Paleoceanography nStratigraphy provides evidence used by scientists to understand changes in the ocean and atmosphere. These include previous circulation patterns, former sea levels, and trends in biological productivity. The Study of Sediments Chapter 14 Pages 14-6 to 14-8

15. MenuPreviousNext 14 - 15 Stratigraphy and Paleoceanography nThe use of stratigraphy and deep-sea drilling has led to a relatively new science; paleoceanography. nPaleoceanography is the study of prehistoric ocean. nPaleoceanographers:  Study chemical ratios and radioactive isotopes found in microfossils to obtain evidence about prehistoric ocean conditions.  Make estimates about prehistoric ocean temperatures and climatic conditions that are thought to be highly accurate. The Study of Sediments Chapter 14 Pages 14-6 to 14-8

16. MenuPreviousNext 14 - 16 Stratigraphy and Paleoceanography nOngoing research of the Earth’s ancient climate currently emphasizes deep ocean sediments called siliceous oozes. nStratigraphy, paleoceanography, and marine geology interrelate with broader studies about the Earth. The Study of Sediments Chapter 14 Pages 14-6 to 14-8

17. MenuPreviousNext 14 - 17 Types of Sediment Chapter 14 Pages 14-10 to 14-15

18. MenuPreviousNext 14 - 18 Sediment Origins nScientists learn a great deal by classifying sediments based on where they come from.  As you may imagine this is important for understanding the processes that created them, the environmental conditions at the time they formed and deposited, and what sorts of deposits they become.  This is why determining sediment origins is one of the cornerstones of paleoceanography.  Sediments may be classified into four origin categories: lithogenous, biogenous, hydrogenous, and cosmogenous. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

19. MenuPreviousNext 14 - 19 Sediment Origins nLithogenous sediments come from the land:  Also known as terrigenous sediments, they result primarily from erosion by water, wind, and ice carrying rock and mineral particles into the sea.  Other lithogenous sediments enter the sea from landslides and volcanic eruptions. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

20. MenuPreviousNext 14 - 20 Sediment Origins nLithogenous sediments make up the majority of sediments found near continents and islands.  This is because they come from weathering and erosion of the land.  Quartz, which is a major mineral - it is hard and does not easily break down physically or chemically.  Feldspar is also abundant in granite.  Clay is common in lithogenous sediments. It consists of small particles that travel far in the water before settling to the bottom. For this reason, clay is often found away from shore. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

21. MenuPreviousNext 14 - 21 Sediment Origins nIt’s estimated that rivers carry up to 15 billion metric tons of lithogenous sediments into the ocean annually.  Human activities, such as agriculture, disturb the land and enhance stream erosion.  Another approximately 100 million metric tons of sediment transfer from land to sea as fine dust and volcanic ash.  Lithogenous sediments usually surround volcanic islands due to the breakdown of basalts and other volcanic rocks that make up the islands. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

22. MenuPreviousNext 14 - 22 Sediment Origins nBiogenous sediments originate from organisms: The particles in these sediments come from shell and hard skeletons. nAlthough lithogenous sediments are the most abundant with respect to their total volume, biogenous sediments cover a larger area of sea floor. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

23. MenuPreviousNext 14 - 23 Sediment Origins nThe vast majority of biogenous sediments come from planktonic organisms that obtain siliceous (contains silica) and calcareous (contains calcium carbonate) compounds from seawater.  These organisms use the compounds to form shells or skeletons, which later settle as sediment when the organisms die.  Some sediment comes from large organisms’ shells and hard corals.  Important deepwater sediments, called oozes, are biogenous. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

24. MenuPreviousNext 14 - 24 Sediment Origins nBiogenous sediments are most plentiful where there’s lots of productivity and where there aren’t a lot of other sediments.  Although organisms are abundant along continental margins where there are ample nutrients, biogenous sediments don’t make up a large proportion of the total sediments in that area.  This is because they are overwhelmed by the loads of lithogenous sediments coming off the continent, especially near the mouths of rivers.  In the deep ocean, where productivity is lower, biogenous sediments are the most common because there are few other types of sediments in the region. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

25. MenuPreviousNext 14 - 25 Sediment Origins nOver time, biogenous sediments accumulate into layers.  Under the right conditions, the organic molecules in these sediments form crude oil (petroleum) and natural gas. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

26. MenuPreviousNext 14 - 26 Sediment Origins nHydrogenous sediments result from chemical reactions within seawater. The reactions cause minerals to come out of solution and form particles that settle on the bottom. nThe sources of the dissolved minerals vary, including the dissolution of submerged rock and sediments, materials coming from new crust forming at mid- ocean ridges, chemicals dissolved in hydrothermal vent water, and material dissolved in river runoff. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

27. MenuPreviousNext 14 - 27 Sediment Origins nHydrogenous sediments accounts for less than 1% of the seafloor sediments, it is the process that produces important mineral deposits, such as ferromanganese and phosphorite nodules. nHydrogenous sediments usually form slowly. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

28. MenuPreviousNext 14 - 28 Sediment Origins nCosmogenous sediments come from outer space. They are primarily made up of small particles the size of sand or smaller called cosmic dust.  Some of these are thought to result from collisions between objects in space, such as asteroids and comets. nCosmic dust particles continually settle through the atmosphere, much as particles settle through water. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

29. MenuPreviousNext 14 - 29 Sediment Origins nMost meteors vaporize before they reach the ground. However, between the settling cosmic dust and meteorites, an estimated 15,000 to 30,000 metric tons of material from space reaches the Earth’s surface each year. nLarge meteor strikes are rare, they can produce tremendous effects locally or even globally, depending on their size. nCosmogeneous sediments are the least abundant of the sediments. Chapter 14 Pages 14-10 to 14-12 Types of Sediment

30. MenuPreviousNext 14 - 30 Sediment Sizes nWhen scientists and engineers need to study how water motion affects sediments, origin is less important than size. nSediments are therefore also classified based on grain size, which is the diameter of an individual particle. nThis classification system identifies sediment ranging in size from a boulder (largest grain size) to clay (smallest grain size). This is shown in the Wentworth Scale. Chapter 14 Pages 14-13 to 14-15 Types of Sediment

31. MenuPreviousNext 14 - 31 Sediment Sizes Chapter 14 Pages 14-13 to 14-15 Types of Sediment

32. MenuPreviousNext 14 - 32 Sediment Sizes nIn addition, scientists sometimes use terms to describe mixes of different grain sizes. For example, mud is a mixture of silt and clay. nAs you may imagine, the smaller a particle, the more easily water motion moves it.  Settling times become longer as particles get smaller. For instance, in water 2 kilometers (1.24 miles) deep, medium sand takes about a day to settle, whereas a clay particle can take 25 years.  Heavy particles require more energy to move and therefore don’t travel as far as fine particles. Chapter 14 Pages 14-13 to 14-15 Types of Sediment

33. MenuPreviousNext 14 - 33 Sediment Sizes nBecause of this, current and waves tend to distribute sediment according to particle size:  Coarse grain sizes are commonly found together in one area with increasingly finer sizes as you move away.  However, this isn’t always the case. This is because other processes affect settling time. For example, clay particles tend to be flat, not spherical like other particles, and are more cohesive (meaning that they cling together) than other particles.  For this reason, clay particles may clump together into larger particles and settle more quickly.  Upwelling water can lift clay and other small particles in the water column and delay settling. Chapter 14 Pages 14-13 to 14-15 Types of Sediment

34. MenuPreviousNext 14 - 34 Sediment Sizes nGrain size and current velocity affect the deposition and erosion of sediment. nSand takes the least amount of energy to erode. nParticles return to the bottom in a roughly linear relationship with the current strength. nSorting results from the nature of water movement in the region. nWhen the water movement does not fluctuate much, sediment tends to be well sorted. nWhen water movement changes frequently, sediment will be poorly sorted. This means that you have sediments with a mix of grain sizes. Chapter 14 Pages 14-13 to 14-15 Types of Sediment

35. MenuPreviousNext 14 - 35 Sediment Sizes Well Sorted Poorly Sorted Chapter 14 Pages 14-13 to 14-15 Types of Sediment

36. MenuPreviousNext 14 - 36 Sediment Sizes Hjulström’s diagram. This shows the relationship that particle size and energy (rate of flow of water or current) have on erosion, transportation, and deposition of sediments. Chapter 14 Pages 14-13 to 14-15 Types of Sediment

37. MenuPreviousNext 14 - 37 Continental Shelf Sediments Chapter 14 Pages 14-16 to 14-19

38. MenuPreviousNext 14 - 38 Sedimentation Processes on the Continental Shelf nTides, waves, and currents strongly control continental shelf sedimentation.  Shoreline turbulence from waves is one of the most notable influences because it keeps small particles from settling.  Surf and waves carry the smallest particles out to sea, which is why most beaches and immediate shorelines are sandy rather than muddy. Continental Shelf Sediments Chapter 14 Page 14-16

39. MenuPreviousNext 14 - 39 Sedimentation Processes on the Continental Shelf Shelf sediments. Idealized model of how sediments are sorted on the continental shelf. Continental Shelf Sediments Chapter 14 Page 14-16

40. MenuPreviousNext 14 - 40 Sedimentation Processes on the Continental Shelf nBecause waves and tides have less effect in deep water, mud can be present further offshore.  As you move toward deep water, sediments tend to have smaller particles.  For this reason, the “ideal” continental shelf sediment would be sand from shore to about 20 kilometers (12.4 miles) out. Continental Shelf Sediments Chapter 14 Page 14-16

41. MenuPreviousNext 14 - 41 Sedimentation Processes on the Continental Shelf nThe sediment would be muddy sand to about 30 kilometers (18.6 miles) out. nGoing further out on the shelf, the sediment would be more muddy and less sandy from sorting. nFrom about 60 kilometers (37.3 miles) from shore out to the edge of the shelf, you would expect to find mud with almost no sand in it. Continental Shelf Sediments Chapter 14 Page 14-16

42. MenuPreviousNext 14 - 42 Recent and Relict Sediments In reality, you don’t find the “ideal” continental shelf you would expect.  Although the expected pattern is evident, you actually find coarse sediment near shore and finer sediment as you follow the bottom deeper and seaward.  Suddenly, you find coarse sediment again.  Moving still further out on the shelf it gets finer and then coarse again. Continental Shelf Sediments Chapter 14 Page 14-17

43. MenuPreviousNext 14 - 43 Recent and Relict Sediments nScientists theorize that this is the result of fluctuations in the sea level over time.  Recent sediments have accumulated since the sea level stabilized.  Relict sediments accumulated and were left stranded when the sea level was lower. Continental Shelf Sediments Chapter 14 Page 14-17

44. MenuPreviousNext 14 - 44 Recent and Relict Sediments Shelf sediments. This model shows how sediments actually occur on the continental shelf. The reason for the intermixing is the effect of past sea level fluctuations. Continental Shelf Sediments Chapter 14 Page 14-17

45. MenuPreviousNext 14 - 45 Continental Shelf Sedimentation Rates nThe sedimentation rate on the continental shelf varies with region. However, in virtually all regions, sedimentation on the shelf is more rapid than in the deep ocean.  At the mouths of large rivers sedimentation can occur at a rate of one meter per thousand years.  Sedimentation is relatively slow along most of the US east coast, despite its many rivers. This is because many of the rivers enter estuaries rather than flow directly into the ocean.  The estuaries trap most of the river sediment. This suggests that the continental shelf sediments off the US east coast are primarily relict sediments left from a lower sea level during the last ice age. Continental Shelf Sediments Chapter 14 Pages 14-17 to 14-18

46. MenuPreviousNext 14 - 46 Continental Shelf Sedimentation Rates nInterestingly, continental shelf sedimentation processes also affect the adjoining deep ocean.  Just as only so much snow can accumulate on a land mountain before it avalanches, accumulating sediment on the continental shelf avalanches down the continental slopes.  These are called turbidity currents.  These deposits are called turbidites.  Turbidity currents travel with so much force that some scientists think they cut the large submarine canyons found on continental slopes. Continental Shelf Sediments Chapter 14 Pages 14-17 to 14-18

47. MenuPreviousNext 14 - 47 Continental Shelf Sedimentation Rates Ice rafting. Glacial sediments are deposited on the sea bottom when rafting ice breaks away from a glacier and floats offshore. As the ice melts, the sediment is released and falls to the bottom and accumulates over time. Continental Shelf Sediments Chapter 14 Pages 14-17 to 14-18

48. MenuPreviousNext 14 - 48 Continental Shelf Sedimentation Rates nThe continental shelves undergo processes that produce biogenous sediments, which also affect the sedimentation rate.  Biogenous sedimentation depends on local productivity, which tends to be high in coastal waters.  Continental shelf sediments tend to have a mix of both biogenous and lithogenous materials.  In tropical climates, calcareous biogenous sediments dominate, especially where there are no rivers to carry in lithogenous sediments. Continental Shelf Sediments Chapter 14 Pages 14-17 to 14-18

49. MenuPreviousNext 14 - 49 Continental Shelf Sedimentation Rates nThe rock cycle includes the formation of sedimentary rock due to compression and chemical processes over millions of years.  Continental shelf sediments appear to be part of this cycle.  Lithification (the formation of rock) sometimes transforms the sediment into rock that eventually becomes part of the terrestrial environment.  Scientists attribute this to the movement of tectonic plates pushing the seafloor up, as well as processes associated with sea level changes.  Much of Florida is made up of sedimentary rock thought to have been marine sediment in the distant past. Continental Shelf Sediments Chapter 14 Pages 14-17 to 14-18

50. MenuPreviousNext 14 - 50 Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-25

51. MenuPreviousNext 14 - 51 Sedimentation Processes on the Deep Ocean Bottom nLike the processes that affect the continental shelf, sedimentation processes in the deep ocean vary regionally.  Since most biological productivity takes place near land, you might expect that seafloor samples taken far from land would have a lower proportion of biogenous material.  Actually, the opposite is true. Deep ocean sediments tend to be high in biogenous material. Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-21

52. MenuPreviousNext 14 - 52 Sedimentation Processes on the Deep Ocean Bottom nThe explanation for this is that there is significantly less lithogenous sediment far from land.  Therefore, proportionately there is a high concentration of biogenous material from planktonic organisms.  Deep ocean sediments that consist of 30% or more biogenous sediment are called ooze.  Oozes have various names, depending on the dominant plankton remains that make them up.  Some planktonic organisms have skeletons or tests made primarily of calcium carbonate.  Oozes composed primarily of these plankton are called calcareous. Other plankton have silica skeletons. They form siliceous ooze. Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-21

53. MenuPreviousNext 14 - 53 Sedimentation Processes on the Deep Ocean Bottom nOozes accumulate slowly. The rate is about 1 to 6 centimeters (0.39 to 2.36 inches) per thousand years. nOoze accumulation rates vary due to several influences.  Amount of organisms at surface.  Rate of Lithogenous sediments accumulate.  Rate at which calcium carbonate dissolves. nClays and other lithogenous materials cover about 38% of the deep-sea floor. Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-21

54. MenuPreviousNext 14 - 54 Sedimentation Processes on the Deep Ocean Bottom nThe variation in deep water sedimentation causes tremendous variations in sediment accumulation.  One of the most conspicuous examples is the differences in sediment thickness in the Pacific and Atlantic Oceans.  Average sediment thickness in the deep Pacific Ocean is half the average thickness in the Atlantic Ocean.  The explanations for this is that the Atlantic has more sediment flowing into it than does the Pacific.  Rivers flowing into the Atlantic drain from wide areas on the continents. Rivers flowing in the Pacific drain less continental area and accumulate less sediment.  Portions of the Pacific have deep trenches that trap sediment - the Atlantic doesn’t have the same deep trenches. Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-21

55. MenuPreviousNext 14 - 55 Sedimentation Processes on the Deep Ocean Bottom Deep-sea deposits around Antarctica. Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-21

56. MenuPreviousNext 14 - 56 Sedimentation Processes on the Deep Ocean Bottom nThe thickness of sediments in the deep ocean also varies with topography.  As previously discussed, sediments are thickest on the abyssal plans and thinnest or absent on the mid-ocean ridges and seamounts. Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-21

57. MenuPreviousNext 14 - 57 Sedimentation Processes on the Deep Ocean Bottom Near-shore and offshore deposition. Deep Ocean Sediments Chapter 14 Pages 14-19 to 14-21

58. MenuPreviousNext 14 - 58 The Carbonate Compensation Depth and Ooze Distribution nThe carbonate compensation depth: It’s an important phenomenon because it explains why, below a certain depth, the characteristics of deep ocean sediments change significantly.  The planktonic organisms that leave behind calcareous tests (skeletons) when they die live everywhere at the ocean surface, yet you don’t find calcareous ooze everywhere in the deep- sea. Deep Ocean Sediments Chapter 14 Pages 14-22 to 14-23

59. MenuPreviousNext 14 - 59 The Carbonate Compensation Depth and Ooze Distribution Carbonate compensation depth. Deep Ocean Sediments Chapter 14 Pages 14-22 to 14-23

60. MenuPreviousNext 14 - 60 The Carbonate Compensation Depth and Ooze Distribution nThis is because seawater contains more carbon dioxide and is therefore more acidic below about 3,000 meters (9,840 feet).  The acidity makes calcium carbonate more soluble in seawater - the tests dissolve. nAbove the calcium carbonate compensation depth, calcareous oozes are the most abundant biogenous sediments. Below it, siliceous oozes dominate. Deep Ocean Sediments Chapter 14 Pages 14-22 to 14-23

61. MenuPreviousNext 14 - 61 The Carbonate Compensation Depth and Ooze Distribution nSiliceous ooze consists primarily of the shells of diatoms and amoeba-like animals called radiolarians.  Their shells dissolve many times more slowly than calcareous tests at all depths.  The slow dissolution of siliceous remains and high diatom productivity allow siliceous oozes to accumulate throughout the seafloor. Deep Ocean Sediments Chapter 14 Pages 14-22 to 14-23

62. MenuPreviousNext 14 - 62 The Carbonate Compensation Depth and Ooze Distribution nAlthough you find siliceous ooze at shallow depths, they are the dominant biogenous sediments below the calcium carbonate compensation depth. nSiliceous ooze is most common in the Antarctic due to strong ocean currents and seasonal upwelling. nSiliceous ooze is also found in equatorial regions west of South America, where diatoms are quite abundant. Deep Ocean Sediments Chapter 14 Pages 14-22 to 14-23

63. MenuPreviousNext 14 - 63 Fecal Pellets nBased on what you learned earlier, you know that the smaller the particle size, the more slowly it settles. nSurprisingly, scientists find that bottom composition is usually similar to the particle composition of the water above it. How can this be? Deep Ocean Sediments Chapter 14 Pages 14-23 to 14-24

64. MenuPreviousNext 14 - 64 Deep Ocean Sediments Fecal Pellets nIt’s because of Fecal pellets - what are they?  Large planktonic organisms, such as copepods, consume the calcareous or siliceous organisms that also dominate the bottom ooze.  These large organisms eliminate their waste as dense fecal pellets of multiple skeletal and shell remains compressed together. Chapter 14 Pages 14-23 to 14-24

65. MenuPreviousNext 14 - 65 Fecal Pellets nAlthough still very small by human standards, these pellets are much larger and sink more quickly than individual skeletal remains. nThey reach the bottom in about two weeks instead of 20 to 50 years. nOn the bottom, the pellets break up from decomposition and chemical processes. Deep Ocean Sediments Chapter 14 Pages 14-23 to 14-24

66. MenuPreviousNext 14 - 66 Mineral Nodules nAn unusual sediment with possible commercial potential is the ferromanganese nodule, which is found mostly in water 4,000– 6,000 meters (13,000–19,700 feet) deep. nThese nodules are irregular lumps about the size of potatoes, though some more than a meter (3 feet) across have been found. nFerromanganese nodules consist of iron and manganese and small amounts of cobalt, nickel, chromium, copper, molybdenum, and zinc. nPhosphorite nodules have also been found. They consist of phosphorite, as well as other trace minerals. Deep Ocean Sediments Chapter 14 Pages 14-24 to 14-25

67. MenuPreviousNext 14 - 67 Mineral Nodules nNodules are hydrogenous sediments thought to be produced by some of the slowest chemical reactions in nature (there are actually three processes thought to account for them). nNodules grow at a rate of 1 to 200 millimeters (0.039 to 7.9 inches) per million years. This makes many nodules 10 or more million years old. nScientists aren’t sure what causes the chemical precipitation that forms nodules. nNodules are found in significant amounts in all the world’s ocean. Deep Ocean Sediments Chapter 14 Pages 14-24 to 14-25

68. MenuPreviousNext 14 - 68 Mineral Nodules Global sediment distribution. Deep Ocean Sediments Chapter 14 Pages 14-24 to 14-25

69. MenuPreviousNext 14 - 69 Sediments as Economic Resources Chapter 14 Pages 14-26 to 14-29

70. MenuPreviousNext 14 - 70 Petroleum and Natural Gas nBy far, oil and natural gas are the most important economic ties to ocean sediments.  Many geological oceanographers work in the gas and petroleum industry.  This is an important component of the world economy.  More than a third of the world’s crude petroleum and a quarter of its natural gas come from sedimentary deposits on the continental shelf.  This is on the rise, with more than $125 billion in annual revenues coming from this source. Sediments as Economic Resources Chapter 14 Pages 14-26 to 14-27

71. MenuPreviousNext 14 - 71 Other Sediments With Economic Importance nMetal sulfides found at deep-sea hydrothermal vents. nSand and gravel. nDiatomaceous earth. nCalcium carbonate. nEvaporites - salts. Sediments as Economic Resources Chapter 14 Pages 14-28 to 14-29